Color detection systems are used to sense polychromatic patterns impressed on a workpiece that carry data in coded form. For example, the polychromatic pattern may be a color bar code having individual bars that vary in color. Color detection systems quantify the colors contained in such polychromatic patterns by illuminating the pattern with broad band spectrum or “white” light and measuring the spectral properties of the reflected light over the entire visible spectrum in comparison with the incident white light spectrum.
Generally, such color detection systems include a halogen lamp that functions as a constant light source of white light that illuminates the polychromatic pattern and one or more individual photodetectors that detect light reflected from the polychromatic pattern and workpiece. Color determination is being made by measuring and quantifying the intensity of the reflected light for different colors. The photodetectors are filtered spectrally using narrow band filters that transmit different wavelength ranges to define colorimetric values with respect to the individual color intensities in the light reflected from the polychromatic pattern. The colorimetric values are supplied to a computer for evaluation of the colors in the polychromatic pattern.
Color detection systems may be used in inspection systems that verify the characteristics of polychromatic printing on a package or carton blank. However, conventional techniques for evaluating the color intensities from such color detection systems are inappropriate due to the high line velocities found in many process lines. These high line velocities make absolute determinations of the shade or hue of a specific product color present in the polychromatic printing problematic because of the sheer number of successive workpieces that must be verified.
Generally, the color of the polychromatic printing determines the manner in which light is reflected from the polychromatic printing. When light is incident upon the workpiece, the reflected light will vary in intensity and wavelength dependent upon the individual colors in the polychromatic printing. The optical properties of the polychromatic printing are also affected by the manner in which light is reflected from the surface of the workpiece bearing the polychromatic printing. Specifically, specular or glossy surface finishes reflect light differently than diffuse objects or those that reflect light in all directions. Conventional color detection systems are especially limited in their ability to evaluate color intensities in light reflected from polychromatic printing on workpieces having specular surface finishes.
It would therefore be desirable to provide an improved inspection device and method for accurately assessing color information contained in polychromatic printing on each of a series of workpieces moving past the inspection device at a relatively high line speed.